It is known that recessive mutant genes in maize can have an effect on the properties of corn starch, and that a recessive gene can be expressed by controlled breeding of maize. Some of these mutant genes which have been identified in maize comprise the genotypes: waxy (wx), amylose extender (ae), dull (du), sugary-1 (su1) and sugary-2 (su2). These recessive genes may be expressed individually or as double-recessive or triple-recessive mutants, such as the amylose extender sugary-2 genotype (aesu2), the waxy sugary-2 genotype (wxsu2), the dull sugary-2 genotype (dusu2) and the amylose extender waxy genotype (aewx). Uses of these double-recessive mutants in foodstuffs have been proposed, as described, for example, in U.S. Pat. Nos. 4,428,972 (wxsu2), 4,615,888 (wxsu2), 4,792,458 (dusu2) and 4,798,735 (aesu2). The published PCT application WO 91/02462 describes uses of the aewx genotype as a thickener in foodstuffs having acidic pHs. It is claimed that starch obtained from this maize genotype shows greater stability in acid foodstuffs, being comparable in that respect to crosslinked waxy starch.
As far as it is known, no patents or publications have described or proposed food uses for sugary-2 (su2) starch, which is obtained from the single recessive maize mutant sugary-2. This sugary-2 mutant was first discussed by Eyster (1934) Bibilographia Genetica, 11:187-392. The sugary-2 gene is located on chromosome 6. The endosperm of sugary-2 kernels ranged from translucent to opaque depending on the number and size of the starch grains developed. The kernels may be slightly or not at all wrinkled. There is no linkage between the sugary-2 (su2) and sugary-1 (su1)-genes. Vineyard et al. (1958) reported an average amylose content of 39% for five sources of su2 mutants, Agron. J., 50:595-598. Mutant kernels are similar to normal kernels in soluble sugar, in water-soluble polysaccharides, and in starch concentrations: Shannon and Garwood (1984), "Genetics and Physiology of Starch Development", pp.25-86, In Whistler et al. (ed.), Starch: Chemistry and Technology, Academic Press, San Diego, Calif.
The gelatinization and retrogradation properties of sugary-2 starch have been studied and compared with other recessive mutant starches. [See Inouchi, et al. (1991) Starch/Starke, 43:468-472, and 473-477.] These investigators found that the expression of the sugary-2 gene reduced starch gelatinization temperatures, and also reduced the heat of gelatinization of retrograded sugary-2 starch.
In acidic foodstuffs which are typically thickened with starch, such as for example, lemon pudding or a lemon pie filling, the thickening and gelling property of the starch tends to be degraded over time due to acidic conditions. There has been a need for starches which are more stable under acid conditions, and which can continue to perform a thickening or gelling function for a longer time at an acid pH. Acid stability is of particular interest for commercial food products which are prepared at a manufacturing plant and distributed and stored in a frozen or non-frozen condition. The desire for such an improved form of starch is illustrated by the recently published PCT application of American Maize-Products Company WO 91/02462 (cited above). This PCT application discloses uses of the amylose extender waxy genotype maize seeds as a source for an aewx-starch useful as a thickener in acidic foodstuffs. Heretofore, as far as it is known, it has not been suggested that a sugary-2 starch could be used as a thickener for acidic foodstuffs.